To summarize: the [Swift Zulian Tiger], [Swift Razzashi Raptor], and [Razzashi Hatchling] are being "removed" because the Raid is being converted into a low-level questing zone.However, Blizzard also added "Although we have no current plans to introduce new ways to obtain the Zul'Gurub mounts, pets, and the tribute mounts, they may return should we find a place where they fit in the future."
While everyone on the WoW forums and websites were claiming that the mounts would be "gone for good" (and to farm ZG as soon as possible), I heard information to the contrary from my inside sources. I had actually predicted this in a post I made last month. =]
Also, although their statement says "no current plans", Blizzard actually does have plans (or should I say "options that they are considering"). The "original mounts" with their "original achievements" will be gone but the mounts will be making a reappearance (as explained earlier) either through drops, rewards (eg Archaeology), the Pet Store, or other ways.
The Pet Store definitely has a very high probability. =]
Also, a little birdie tells me that a mount similar to the [Black Qiraji Battle Tank] will be making an appearance in Cataclysm as well. My sources weren't as certain on the new scarab mount as they were on the ZG mounts, however.